(1) Field of the Invention
The present invention relates to finely divided silicon carbide having a high content of 2H-type silicon carbide, a method of producing the silicon carbide, a high-density silicon carbide sintered body produced from the silicon carbide and a method of producing the silicon carbide sintered body.
(2) Description of the Prior Art
Silicon carbide is used in gas turbine, heat exchanger and the like as a best material for improving the high-temperature strength and thermal shock resistance thereof, and further used as a lining material for ball mill and as parts of burning tube and of instruments for handling corrosive liquid and liquid metal.
Silicon carbide has hitherto been considered to be a hardly sinterable material. However, it has recently been found out that a mixture of .beta.-type submicron silicon carbide and sintering aids of boron and carbon can be sintered into a high-density sintered body having a given shape by a pressureless sintering process. However, this process requires a temperature higher than 2,000.degree. C. in order to obtain a sintered body having substantially a high density. Such high sintering temperature requires a severe operation condition and is disadvantageous in the commercial production of the sintered body, and further often forms coarse plate-like particles having a size of as large as 200 .mu.m in the resulting sintered body. Sintered bodies composed of particles having the smaller size have the higher mechanical strength, and the presence of large-size particles decreases the strength of sintered body. Accordingly, the formation of coarse particles must be suppressed as possible. However, when the sintering temperature exceeds 2,000.degree. C. 6H-type silicon carbide is apt to be formed due to .beta.-.alpha. transformation. The 6H-type silicon carbide grows at a rate fairly higher than the rate of growth of .beta.-type silicon carbide, and therefore the 6H-type silicon carbide is once formed due to the transformation, coarse particles grow during the sintering and are contained in the resulting sintered body. In order to suppress this phenomenon, it has been attempted to blow nitrogen having an effect for suppressing the .beta.-.alpha. transformation into the sintering atmosphere at high temperature. However, such process requires a temperature higher than that required in the case where nitrogen is not blown into the atmosphere, and requires more severe operation condition.